6TB drives that's SIX TeraBytes!

All the math in these articles assume the drives don't exceed the URE specs on their datasheets. That is perhaps questionable - some drives are far worse than their datasheets, others seem to outperform. I am also not convinced that an unrecoverable read error is a random event (which is also tacitly assumed by the statistics). I expect a healthy drive to have no UREs, and the UREs begin to happen as the drive fails.

If you read these forums, you will see many cases where disk errors occur during RAID recovery - requiring users to recover data from backup, or attempt to clone drives to conceal the errors. Personally I continue to use RAID-5 on my Pro, and maintain full multiple backups of the data.

The decision to go with single/dual redundancy should based on the need to keep the data available during disk replacement (or the convenience of avoiding recovery from backup as much as possible). Dual redundancy fails much less often, but you still need backups even with RAID-6.